What you should do is stop playing nice with somebody who evidently has no problem with being dishonest. You already stated that you have a rule:

A student who plagiarizes twice will receive zeros for the assignments and may withdraw or take an F for the course.

All you have to do is apply it, I don't understand what you could possibly perceive as "tricky" here.

What you should do is stop playing nice with somebody who evidently has no problem with being dishonest. You already stated that you have a rule:

A student who plagiarizes twice will receive zeros for the assignments and may withdraw or take an F for the course.

All you have to do is apply it - I don't understand what you could possibly perceive as "tricky" here.

What you should do is stop playing nice with somebody who evidently has no problem with being dishonest. You already stated that you have a rule:

A student who plagiarizes twice will receive zeros for the assignments and may withdraw or take an F for the course.

All you have to do is apply it.

What you should do is stop playing nice with somebody who evidently has no problem with being dishonest. You already stated that you have a rule:

A student who plagiarizes twice will receive zeros for the assignments and may withdraw or take an F for the course.

All you have to do is apply it, I don't understand what you could possibly perceive as "tricky" here.